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Financial Instruments - Outstanding Forward Agreements to Purchase Foreign Currency (Detail) - MXN ($)
 9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items]    
Fair Value Asset   $ 2,605,000,000
Forward agreements to purchase foreign currency [member]    
Disclosure of detailed information about financial instruments [line items]    
Maturity Date 2019 2019
Notional Amount $ 3,301,000,000 $ 4,768,000,000
Fair Value (Liability) (31,000,000) (66,000,000)
Fair Value Asset $ 83,000,000 $ 109,000,000
Forward agreements to purchase foreign currency [member] | Later than one year and not later than two years [member]    
Disclosure of detailed information about financial instruments [line items]    
Maturity Date 2020  
Notional Amount $ 4,323,000,000  
Fair Value (Liability) (17,000,000)  
Fair Value Asset $ 58,000,000  
Options to purchase foreign currency [member]    
Disclosure of detailed information about financial instruments [line items]    
Maturity Date 2019 2019
Notional Amount $ 245,000,000 $ 1,734,000,000
Fair Value (Liability) (2,000,000) (33,000,000)
Fair Value Asset $ 9,000,000 $ 57,000,000
Options to purchase foreign currency [member] | Later than one year and not later than two years [member]    
Disclosure of detailed information about financial instruments [line items]    
Maturity Date 2020  
Notional Amount $ 112,000,000  
Fair Value Asset $ 8,000,000